1-2 Shift Valve
WARNING: This page is about a different car, the 2009 Cadillac DTS. However, it is still accessible from the selected car via links, so may be relevant.
High fluid pressure in 2-3 shift solenoid (SS) valve holds the 1-2 shift valve in the upshifted position. The 1-2 shift valve allows fourth band feed fluid to enter the fourth band circuit. Fourth band fluid is then routed to the 3-4 accumulator piston and to the fourth servo piston.